In British patent 932189 (Hodgkinson) issued in 1963 is shown a farrowing crate or pen for sows where the level of the outer floor section which carries the piglets can be raised and lowered in order to move the piglets away from danger from the sow when the sow is standing. Thus when the sow lies down, the piglets are kept away from the height of the floor level on which the sow lies to reduce the possibility of crushing.
This arrangement uses a light beam and electric switches to detect the movement of the sow and uses a complex lifting arrangement. The device is currently not available on the market.
U.S. Pat. No. 4,793,287 of Hoffmann issued in 1988 discloses a modified arrangement in which lifting and lowering of the piglet floor section is actuated by an alternative arrangement. However again this construction is disadvantageous and is not available in the market place.
In German Application DE 43 20 345 (Ulrich) published 22nd Dec. 1994 is disclosed a farrowing pen with a base frame which is laid on a floor with an air bag carried on the base frame which can be actuated to raise a sow support floor section mounted on top of the base frame on levers which swing the floor section longitudinally and upwardly. The lifting action is controlled by a valve which actuated by the sow lying down on the valve or standing up from the valve.
In European Application 360 308 (Geerkens) published 28 Mar. 1990 is disclosed a farrowing pen with a lift frame mounted over a sow support floor section for lifting the floor section upwardly on two motors and associated screws, one at each end. The lifting action is controlled by a photo-electric cell which detects lying or standing of the sow.